Question

Which were dominant in Mesozoic?
A) Dinosaurs
B) Gymnosperms
C) Fishes
D) Mammals

Answer 1

Each era in the evolution of the earth as a complex ecosystem was dominated by different life forms and also had several periods of mass extinction, one of which was responsible for the dying out of dinosaurs.

Complete answer:
The Mesozoic era lasted for around 180 million years. Dinosaurs evolved during the Triassic period, and were most dominant during the Jurassic age, dying out at the end of the cretaceous period. They were the most dominant form of life during this era. Option A is therefore the correct answer.
Option B is not correct. Terrestrial vegetation also became more and more complex during this time. Ferns, cycads, and other such non-woody plants evolved. Even though gymnosperms did appear during this period, angiosperms also started to take over and gradually became more dominant that the gymnosperms. However, as plants they did not dominate over dinosaurs. Gymnosperms were also a part of the diet of herbivorous dinosaurs.
Option (C) is also incorrect. Fishes were continuing to evolve, along with many other invertebrates, but the dominant form in the oceans was still the reptiles.
Option (D) is also wrong. Mammals did live alongside dinosaurs, but they were much smaller in size. They did not truly start to evolve into large predators and become more complex till the dinosaurs died out at the end of the cretaceous period. They became much more successful as being homoeothermic; they could survive greater changes in weather.

Hence the correct answer is OPTION(A)

Note: While dinosaurs are considered to be extinct, with the oldest species of reptiles being the turtles and crocodilians, they are said to have survived in the form of modern-day birds. Though warm-blooded, birds are closely related to dinosaurs.